There are thousands of subsea structures connected with the drilling and production of oil and gas from oil and gas wells which are now characterized as abandoned. Non-limiting examples of such subsea structures include wellheads, casing stubs, etc., which either extend above the mudline (seabed) or are close to the mudline. The subsea structures can vary from simply a relatively large diameter piece of pipe to more complex structures comprised of concentric steel pipes, the annulus between which are filled with concrete or cement.
Federal guidelines for the removal of such subsea structures in offshore water under United States jurisdiction typically mandate that the structure must be cut off 15 feet below the mudline unless a variance is obtained. Typical methods of removing subsea structures include explosive removal, thermal lances, electrodes for subsea cutting, grinders, pipe cutters, etc. However, because of the mandate that the subsea structure must be cut off 15 feet below the mudline, in many cases divers and other highly trained personnel must be employed to excavate around the subsea structure down to the desired depth and then carry out the cutting operation. Clearly such operations are tiresome, expensive and involve considerable fatigue and risk for the operating personnel.
U.S. Pat. Nos. 3,056,267 and 5,361,741 disclose methods and apparatus for cutting subsea structures.